Method of self-aligned double patterning

1. A method of self-aligned double patterning, comprising: providing a substrate, wherein a hard mask layer formed on said substrate; forming multiple mandrels on said hard mask layer and forming spacers at two sides of each said mandrel, wherein said mandrels extend in a first direction and first trenches are formed between said spacers and extend into said hard mask layer by a vertical thickness; forming a protection layer filling up said first trenches; removing said mandrels to form second trenches exposing said hard mask layer between said spacers; and performing a first anisotropic etch process using said spacers and said protection layer as an etch mask to remove a portion of said hard mask layer exposed from said second trenches.

2. The method of self-aligned double patterning of claim 1 , wherein said first anisotropic etch process removes a portion of said hard mask layer exposed from said second trenches, so that a thickness of said hard mask layer exposed from said second trenches equals to a thickness of said hard mask layer under said protection layer.

3. The method of self-aligned double patterning of claim 1 , wherein the steps of forming said spacers comprises: forming a conformal spacer layer on said mandrels and said hard mask layer; and performing a second anisotropic etch process to said spacer layer, so that said spacer layer self-alignedly transforms into said spacers at two sides of each said mandrel and forming said first trenches exposing said hard mask layer between said spacers, wherein said second anisotropic etch process concurrently remove a portion of said hard mask layer exposed from said first trenches, so that said first trenches extend into said hard mask layer by said vertical thickness.

4. The method of self-aligned double patterning of claim 1 , further comprising removing said protection layer and said spacers after said first anisotropic etch process to expose entire said hard mask layer, wherein said hard mask layer is provided with multiple protruding line patterns spaced apart from each other and extending in said first direction.

5. The method of self-aligned double patterning of claim 4 , further comprising: performing a preceding self-aligned double patterning process before forming said hard mask layer to form multiple preceding line patterns spaced apart from each other and extending in a second direction; forming a dielectric layer and said hard mask layer on said preceding line patterns; and performing a third anisotropic etch process to said hard mask layer after said protection layer and said spacers are removed to transfer said line patterns of said hard mask layer to said preceding line patterns under said line patterns, so that overlapped said line patterns and said preceding line patterns form multiple dot mask patterns arranged in an array on said substrate.

6. The method of self-aligned double patterning of claim 1 , further comprising performing a trimming process after said mandrels are removed to trim and adjust a thickness of said spacers and a width of said second trenches.

7. The method of self-aligned double patterning of claim 1 , wherein said mandrel comprises an organic dielectric layer and a dielectric anti-reflective coating, and said first anisotropic etch process concurrently and completely removes said anti-reflective coating of said mandrel.